Interactions between Azotobacter vinelandii nitrogenase and the Fe protein from Clostridium pasteurianum and between the nitrogenase of C. pasteurianum and the MoFe protein from A. vinelandii are being studied to determine the nature of the binding of nitrogenase components, the ratio of components bound and the functioning of nitrogenase components when bound or separate. The kinetics of nitrogenase from A. vinelandii are under investigation to aid in determining the mechanism of action of nitrogenase. Studies on the physiology of Spirillum lipoferum and on the nature of its nitrogenase are aimed at improving its N2-fixing relationship with a variety of nonleguminous plants. The Fe protein in the nitrogenase from Rhodospirillum rubrum requires an activating factor; this factor is being purified and its mode of action is under investigation. The organic acid metabolism of roots under low oxygen concentrations is being studied to determine how this may influence the proliferation and activity of S. lipoferum in roots. Isolated heterocysts from the N2-fixing blue-green alga, Anabaena, evolve H2 and take up H2; their metabolism of H2 is being investigated to determine how it is related to their N2 fixation and how H2 uptake is coupled to ATP formation. BIBLIOGRAPHIC REFERENCES: Burris, R.H. Nitrogen fixation by blue-green algae of the Lizard Island area of the great barrier reef. Aust. J. Plant Physiol. 3, 41-51 (1976). Peterson, R.B. and Burris, R.H. Properties of heterocysts isolated with colloidal silica. Arch. Microbiol. 108, 35-40 (1976).